Stoker control



p 1940- F. s. DENISON ET AL 2,215,067

STOKER CONTROL Filed Aug. 17, 1956 Patented Sept. 17, 1940 STOKER CONTROL Application August 1'1, 1936, Serial No.96,390

19 Claims.

The present invention relates to a stoker con- 1 trol and more particularly to one employing temperature sensitive elements located in the fuel bed.

5 It has been found desirable to control a motor operated stoker for a coal fired furnace by conditions in the furnace as well as by conditions in the space being heated. Thus, it has been found desirable in the prior art to provide an out fire control wherein the operation of the stoker motor is prevented when combustion has ceased or become diminished to such a point that additional fuel, if supplied, would not be ignited. It has further been proposed to provide a "hold fire control wherein the stoker motor is placed in operation regardless .of the demand of the room thermostat whenever combustion has reached such a low point that it is imperative that fuel be added in order to continue the fire. It has also been proposed to provide some means responsive to excess temperature conditions to prevent the operation of the stoker motor when such conditions prevail.

In the usual prior art installations of the type previously referred to, the various controls responsive to conditions in the furnace are located remote from the fuel bed, being responsive to such conditions as stack temperature. Since all of the various conditions referred to are primarily conditions within the fuel bed itself, such location of the controlling instruments at other points results in an indirect measurement of the controlling conditions which may often lead to unsatisfactory operation. While it has been proposed in one instance to locate the temperature responsive elements in the fuel bed itself, these elements have all been located at substantially the same position and were made dependent upon a variation in temperature in this location. Even this 0 is not a direct measurement of the conditions which it is desired to have controlled by the stoker motor. For example, in the case of an out fire control, it is not so important what the temr perature is in some normally constant temperature zone but rather whether combustion is taking place at a point where combustion will always take place if there is any combustion whatsoever. Similarly, in the case of the "hold fire 50 control, the important question is how far combustion has spread rather than what the :temperature is in a normally constant temperature zone.

An object of the present invention is to provide 55 a stoker control wherein the control of the stoker matically.

is, in part at least, determined by the extent to which combustion has spread in the fuel bed.

A further object of the present invention is to provide a stoker control employing a plurality of temperature responsive devices located in the fuel bed at various points from the center of combustion so as to indicate the extent of the zone of combustion.

A further object of the present invention is to provide a stoker control employing thermo-couples embedded in the fuel bed and acting as temperature responsive elements to control a stoker motor. I

A further object ofthe present invention is to provide an electrical device, the energization of 15 which is controlled by a pair of opposed thermocouples so that upon the junction of either one of the thermo-couples being heated, the device is energized but upon the junction of either both or none of the thermo-couples being heated, the 20 device is deenergized.

A further object of the present invention is to provide a switch with means to oscillate the switch without changing the circuit controlling position until a holding means is effective to 25 cause the switch to be moved to a different circuit controlling position by the oscillating means and wherein upon the switch being so moved, the oscillating means is not effective upon said switch even though it continues to operate. 30

A further object of the present invention is to provide means in a thermo-couple energized controller for temperature changing apparatus which is efiective to require a differential in temperature between energized and deenergized con- 35 ditions of the said controller.

Other objects of the present invention will be apparent from a description of the accompanying specification, claims and drawing.

In the single view of the drawing the stoker 40 control of the present invention is shown sche- Referring to said drawing, a portion of a coal furnace is shown in section and is designated in its entirety by the reference numeral Ill. The 46 furnace comprises an outer jacket H and an inner jacket I2, which inner jacket serves to support a grate l3 in the usual position. Extending through a center portion of the grate I3 is the flared end It of a conveyor duct l5 which serves 50 to supply coal to the furnace, feeding it onto the grate IS. The coal is moved through duct l5 by a conveyer screw 16 which is driven by a motor 11. The coal is stored in a hopper l9 from which it passes into duct l5. 7

Extending through the grate are a plurality of thermo-couples 20, 2|, 22, and 23. As will be noted from the drawing, the thermo-c'ouples 2| and 22 are connected in opposition and are adapted to cooperate to control a switch 24. Similarly, thermo-couples 20 and 23 are also connected in opposition and are adapted to cooper-.-

The disc 60 is secured to a shaft 6| driven by a motor 62 of any suitable construction, through a suitable reduction gearing 63. The motor 62 is provided with a winding 65 which is connected" to line wires 66 and 61 through conductors 68 5 and 69. A manual switch 10 is preferably interposed in the conductor 68 to: provide some means ate to control aswitch 25. Each of these thermocouples comprises a pair of members of different thermo-electric characteristics, the junction of which is located in the fuel bed.

This junction would constitute the hot junction of the thermo-couple if the thermo-couple were not connected in opposition with another thermo-couple. Due to the fact, howe'venthat when the thermo-couples are so connected the Junction of one thermo-couple may actually constitute a cold junction of the group, the point in each unit at which the two members of different thermo-electric characteristics are physically connected together is referred to hereinafter merely as the junction of that thermo-couple.

The structure of switch 24 will first be described. The switch proper comprises two contact carrying blades 30 and 3|. The contact carrying blade 3| has secured thereto a contact 32 and the contact carrying blade 39 is formed with a contact carrying member 33 which extends upwardly and forwardly over contact 32 and carries a contact 34 which is adapted to engage contact 32. Also secured to contact carrying arm -3| is an armature 36 which is adapted to" cooperate with an electromagnet 31. The electromagnet 31 is provided with a ,main winding 38 and an auxiliary winding 39. The main winding 38 is connected through conductors 44 and with the oppositely-connected thermo-couples 2| and 22. When the junction of thermo-couple 2| is heated but the junction of thermo-couple 22 is not, winding 38 will be energized. When the junctions of both thermo-couples are subjected to fiame, they will oppose each other and the winding 38 will be deenergized.

The auxiliary winding 39 is energized through a transformer 40; the primary 4| of which is connected in parallel with the stoker motor IT. The secondary 42 of transformer 40 is connected to the input terminals of a rectifier 43 which is shown for purposes of illustration as an ordinary bridge rectifier. The output terminals of rectifier 43 ,areconnected through conductors 46 and 41 to auxiliary winding 39. It will be readily seen that inasmuch as the primary 4| of transformer 48 which controls the energization of auxiliahy winding 39 isv connected in parallel with motor I! that winding 39 will be energized whenever the motor. I! is energized. The winding 39 is so conto limit movement of arm 53 to the left.

nected' to-the output terminals of rectifier 43 that it will aid winding 38 when energized. The purpose of the rectifier is to insure that the current through winding 39 will be unidirectional and hence that winding 39 will always aid winding 38.

by reason of both thermo-couples 2| and 22 being heated or by reason of neither of these thermo-couples being heated. As the apparatus is shown in the drawing, the deenergization of winding 38 is due to the fact that both of the 20 thermo-couples 2| and 22 are subjected to the same temperature of combustion adjacent their hot junctions.

The motor 62 is efiective to continuously rotate disc 60 in a clockwise direction with the result 2 that pin 59 periodically engages the arm 5|. Upon pin 59 engaging arm 5|, the arm is moved upwardly and at the same time is pivoted about 52 due to the fact that the pin 59 is retained in engagement with the end 58 of arm 5| by reason 30 of the'inter-engaging curved surfaces; Before disc 60 has rotated to the point where pin 59 lies on a line extending between the center of disc 60' and pivot-point 52, the'armature 36' has arm 50 and the spring 55 will be effective to return arm 5| to the radial position shown in the draw-" 40 ing. If the windings 38 are not energized when armature 36 is moved into engagement with the electromagnet, pusher members i 58 will drop again allowing members 30 and 3| to move to the position shown in the drawing. In view of the 45 fact that the member 3| is biased downwardly, any upward movement imparted thereto .by rea-v son of the pusher mechanism 59 will not cause v the contacts 32 and 34 to be moved into engagement. Thus, armature 36 is moved into engage- 5o ment with electromagnet 31 without disturbing- ;the relative position of contacts 32 and 34. Sim-.-

out changing the controlling position of switch 24. except when the armature 36 is held bythe electromagnet 31. In view of the factthat switch 25 is identical in construction with switch 24,-

Secured to contact carrying blade 30 is a pusher member 50 which has anarm 5| pivotally secured thereto at 52. A pin 53 extends from arm 5| and engages a shoulder of member 50 so as spring 55 is secured at one end to arm -5| and at the other end to an extension 56 of pusher member 59-and serves to hold arm 5| in its extreme left-hand position with pin 53 in engagement with its cooperating shoulder portion. Arm

with the exception that no auxiliary winding is employed on the magnet, and is shown in-the position in which armature 36 is held in engagement with magnet 31, this switch will now be described in order to obtain'a clearer un der standing as to the operation of the switchupon the armature being held by the electromagnet.

.In view of the fact that, as previously mentioned, the structure of the switches 24 and '25- is identical, with the exception of theauxiliary winding, the elements of switch 25 correspond ing to those of switch 24 have been assigned reference numerals which are exactly one hundred higher than the corresponding elements of switch 24. Further, in view of the fact that the character of the elements referred to by these reference numerals is obvious in view of the preceding description of switch .24, it is deemed unnecessary to specifically describe this structure except as is incidently done in connection with a description of the operation thereof. 1

In a manner similar to the method in which switch 24 is oscillated, the switch 25 is actuated by reason of a pin I59 on a disc I60 driven by shaft 6| periodically engaging the curved end I58 of arm I5I. As in the case of switch 24, contact I32 carried by contact carrying member I31 is not moved into engagement with the contact I34 carried by contact carrying member I30 during such oscillation of the switch through disc I60 and pusher member I50, unless armature I36 is held by the'magnet I31. As previously mentioned, armature I36 is so held in the position shown in the drawing. Upon member I36 having been initially moved into engagement with magnet I31 by the pin I59 acting on arm I5I and consequently pusher I50, contacts I32 and I34 are still separated. Upon the armature I36 being so held, contact carrying member I3I is held against downward movement. As soon as the pin I59 has rotated sufliciently in a counter-clockwise direction to ride from underneath the curved end I58 of arm I5 I, pusher member I50 is released permitting contact carrying member I30 to move downwardly until the contact I34 is moved into engagement with contact I32. Further downward movement of contact carrying member I30 is prevented by reason of the engagement of contacts I 32 and I 34.

It will be noted that the curved end I58 of arm I5I is in a position wherein pin I59 will not engage the same. This is due to the fact that member I30 is held in an elevated position by reason of the engagement of contacts I32 and I34 with the result. that pusher member I50 is also held in an elevated position. The apparatus is so designed that when the pusher member I50 is held in such an elevated position and the arm I5I is retracted by reason of the spring I55 secured between extension I56 and arm I5I, the curved end I58 will be raised sufilciently to be out of the path of pin I59. If this were not done, contact member I30 would be oscillated by member I60 after engagement of contacts I32 and I34 causing the periodic disengagement of these contacts.

In addition to the controlling switches 24 and 25, a thermostatic switch I10 is provided. This thermostatic switch may take any desired form and may preferably be located in the space being heated, functioning as a room thermostat. The thermostat I10 is shown for purposes of illustration as comprising a bimetallic element I1I to which is secured a contact blade I12 adapted to cooperate with a fixed contact I13. A magnet I14 is designed to cooperate with contact blade I12 and hold the same slightly when the blade is moved into engagement with contact I13, thus preventing immediate disengagement of blade I12 from contact I13 upon the temperature rising.

In general it may be stated that switch 25 is connected in the circuit of stoker motor I1 in series with both thermostatic switch I10 and switch 24 while switches 24 and I10 are connected in parallel. Further, it may be stated that switch 25 functions as a combined "out fire" and high limit" switch whereas switch 24 functions as a "hold fire switch.

As previously indicated, the various elements are in the position assumed when combustion has spread to a point where the junctions of both thermo-couples 2I and 22 are heated. Moreover, combustion has not reached the point where the junction of thermo-couple 23 is heated. In other words, combustion has spread sufllclently far that it is above the minimum range during which the hold fire switch is closed and is below the maximum at which the high limit switch is open, so that the stoker motor is under the sole control of the thermostat I10. The thermostat I10 is moreover shown in open position, or in other words, it is shown in the position assumed when the temperature in the space being heated is at or above the desired value. Upon the temperature falling below the value for which the thermostat is set, the contact blade I12 will be moved into engagement with contact I13, being held in engagement therewith by magnet I14. Upon this taking place, the following circuit is established to stoker motor I 1: from line wire 61 through conductor I16, switch 25, conductors I11 and I18, thermostat I10, conductors I19, I 80, and I8I, stoker motor I1, and conductors I82 and I83 to line wire 66.

So long as the limit of the zone of combustion remains between the hot junction of thermo-couples 22 and 23, the stoker will be under the sole control of the thermostat I10 and stoker motor I1 will operate only so long as thermostatic switch I10 is closed. Upon the temperature rising sufllciently that contact arm I12 is moved away from contact I13 against the action of magnet I14, the previously traced circuit to the motor I1 will be interrupted so that motor I1 will be placed out of operation. During normal action of the stoker, the making and breaking of the previously traced stoker motor circuit in the manner just described is substantially the only controlling operation taking place.

If, however, due to an excessive heat loss such as caused by a window being open or for some other reason, the thermostat I10 continues to call for heat" for an excessively prolonged period, it may well happen that combustion reaches such an excessively high value that the junction of thermo-couple 23 is heated. When this takes place, the thermo-couples 20 and 23 will be generating electromotive forces which are in opposition to each other. The result is that the energization of winding I38 will be decreased to such a point that the electromagnet I31 is not effective to hold armature I36. When this happens, both contact arms I30 and I3I move downwardly until they assume the position in which the corresponding elements of switch 24 are shown. In this position, contacts I32 and I 34 will be separated so that switch 25 is opened. In view of the fact that switch25 is in series with both switch 24 and thermostat I10, it is impossible to establish a circuit to the stoker motor I1 so long as switch 25 is open. In this manner, it is assured that in the event of combustion spreading to an excessive extent, the further operation of the stoker motor is prevented. Since the ther mo-couple is located in the fuel bed and is dependent upon the spread of combustion, it is able to det ct a condition leading to excessively high temperatures before the high temperature has actually been produced. In this manner, it functions to anticipate an undesirable condition instead of acting only after the undesirable condition has been produced.

The condition which has just been described is that arising when thermostat III] is closed an excessive amount of the time. If, on the other hand, the thermostat I'III only seldom calls for heat, such as might be the case in mild weather, it is possible for the coal supplied to the furnace to be insufficient to support continued combustion. Since it would be highly desirable to prevent the fire from going out under such conditions, the thermo-couples 2I and 22 are provided, which function as a hold fire control. In a manner similar to the hold fire controls of the prior art, these thermo-couples are effective to cause the closing of a switch in parallel with a thermostat when combustion has been reduced to the point that it is imperative that more coal be added to prevent extinguishing of the fire. In the present case, the switch in parallel with the thermostat is switch 24. If combustion recedes to the point where the temperature of the junction of thermo-couple 22 is reduced substantially, the winding 38 will be energized in view of the fact that the electromotive force produced by thermo-couple 2| is not appreciably opposed by that produced by thermocouple 22. The result is that electromagnet 31 is energized and upon armature 36 being moved into engagement therewith through the action of the mechanism including disc 50 and pusher member 50, previously described, the armature 36 will be retained thereby. This will cause contacts 32 and 34 to be moved into engagement in the manner described in connection with switch 25 so that switch 24 is closed. A circuit will then be established to stoker motor II as follows: from line wire 61 through conductor I16, switch 25, conductor I'II, conductor I85, switch 24, conductors I86, I80 and I'8I, stoker motor I1 and conductors I82 and I83 to the other line wire 66. It will be noted that the circuit just traced is independent of thermostat IIO so that stoker motor I! is operated even through thermostat I10 is satisfied. The circuit just traced will be maintained until coal has been supplied to the fuel bed and combustion has spread sulficiently to cause the junction of thermo-couple 22 to again be heated.

In order to insure that switch 24 will not be rapidly closed and opened by reason of a slight variation in combustion around thermo-couple 22, the arrangement comprising auxiliary winding 39 is provided. As soon as switch 24 is closed by reason of the energization of winding 38, the motor I1 is placed in operation as previously described. Upon this occurring, the transformer 40 is also energized with the result that winding 39 is energized in a direction to aid winding 38. The winding 39 exerts a sufficient holding action that it is necessary for the temperature of junction 22 to cool appreciably below the point at which closing of switch 24 was effected before switch 24 will open. In other words, by reason of the winding 39, it is insured that a differential in temperature is required between the closed and open positions of switch 24.

Both thermo-couples 20 and 2| are located sufficiently close to the point at which fuel is supplied to the fuel bed that the junctions of both of these thermo-couples are normally maintained heated. If, however, for some reason or other, the zone of combustion is so reduced that even these thermo-couples are not energized,

the operation of stoker motor I1 is again prevented. This Il desirable because under these conditions the addition of further fuel is undesirable since it would not be ignited. If some means were not provided for stopping the operation of the stoker motor, the thermostat or the hold fire control would continue to call for operation of the stoker and coal would be supplied continuously to the furnace. When the temperature of the junction of thermo-couple 22 is reduced due to the zone of combustion receding in the manner previously described, winding I38 will be deenergized due to the fact that the junction of neither thermo-couple 20 nor 23 is being heated so that no electromotive force is being produced in the circuit including winding I38. Under these conditions, switch 25 is opened. As prevously described, since switch 25 is in series with the switches 24 and III), the opening of this switch prevents operation of stoker motor I I regardless of whether thermostat I10 or switch 24 is closed.

It will be seen that means has been provided for controlling a stoker motor wherein the temperature responsive means is responsive to the spread of combustion rather than to a change of temperature at any point. In this manner, the conditions which should control are measured directly. Furthermore, a stoker control has been provided employing thermo-couples which are of particular adaptability to the high temperature encountered in the fuel bed of a furnace. Moreover, there has been provided a novel arrangement wherein a pair of thermo-couples are connected in opposition to energize an electrical instrument so that upon either one of the thermocouples being subjected to a temperature differential between its hot and cold junctions, the device is energized but upon both or none of the thermo-couples being subjected to such a differential, the device is deenergized. Furthermore, there has been provided in a switch which is oscillated without changing its circuit controlling position until a holding means is effective to change the circuit controlling position, means for preventing the oscillating means from being effective after the circuit controlling position of the switch has changed. It will further be noted that there has been provided a novel arrangment for providing a differential between the energized and deenergized positions of a thermocouple operated instrument.

While there has been shown a certain specific embodiment of the invention, it is to be understood that this is for purposes of illustration only and that the invention is to be limited only by the scope of the appended claims.

I claim as my invention:

1. In combination, a fuel burning device comprising a fuel supporting surface, means for feeding fuel onto said supporting surface, and means controlling the operation of said fuel feeding means including a plurality of temperature responsive devices each responsive to the temperature, at a predetermined point, of the fuel located on said fuel supporting surface, said temperature responsive devices being disposed at varying distances from the point at which fuel is supplied to said surface so as to control said fuel feeding means in accordance with the extent to which said fuel is ignited.

2. In combination, a fuel burning device comprising a fuel supporting surface, means for feeding fuel onto said supporting surface, and means controlling the operation of said fuel feeding means including a pair of opposed thermocouples e'ach-responsive to the temperature, at a predetermined point, of the fuel located on 'said fuel supporting surface, said thermo-couple devices being disposed at different distances from the point at which fuel is supplied to said surface so as to control said fuel feeding means in accordance with the extent to which said fuel is ignited, only one of said thermo-couples generating an appreciable electromotive force when the boundary of ignited fuel is between the thermo-couples and both generating an electrometive force when ignited fuel is adjacent both thermo-couples.

3. In combination, a fuel burning device comprising a fuel supporting surface, means for feeding fuel onto said supporting surface, electrically operated means controlling the operation of said fuel feeding means and effective when energized to cause fuel to be supplied by said fuel feeding means, energizing means for said controlling means including a pair of opposed thermo-couples disposed to extend into fuel located on said fuel supporting surface, one of said opposed thermo-couples having the junction thereof located adjacent the point at which fuel is supplied to said surface so as to be energized so long as there is any combustion whatsoever and the other of said thermo-couples having the junction thereof located adjacent a point on said supporting surface sufficiently remote from the point at which fuel is supplied thereto so as to be energized only when combustion has reached a predetermined high limit.

4. In combination, a fuel burning device comprising a fuel supporting surface, means for feeding fuel onto said supporting surface, electrically operated means controlling the operation of said fuel feeding means and effective when energized to cause fuel to be supplied by said fuel feeding means, energizing means for said controlling means including a pair of opposed thermocouples disposed to extend into fuel located on said fuel supporting surface, one of said opposed thermo-couples having the junction thereof located adjacent the point at which fuel is supplied to said surface so as to be energized so long as there is any combustion whatsoever and the other of said therrno-couples having the junction thereof located adjacent a point on said supporting surface sufficiently remote from the point at which fuel is supplied thereto so as to be energized only when combustion has extended sufficiently far to insure continued combustion without the immediate addition of further fuel.

5. In combination, a fuel burning device comprising a fuel supporting surface, means for feeding fuel onto said supporting surface, electrically operated means controlling the operation of said fuel feeding means and effective when energized to cause fuel to be supplied by said fuel feeding means, energizing means for said controlling means including a pair of opposed thermocouples disposed to extend into fuel located on said fuel supporting surface, one of said opposed thermo-couples having the junction thereof located adjacent the point at which fuel is supplied to said surface so as to be energized so long as there is any combustion whatsoever and the other of said thermo-couples having the junction thereof located adjacent a point on said supporting surface sufficiently remote from extended sufficiently far to insure continued combustion without the immediate addition of further fuel, and further means responsive to adifferent controlling condition for controlling the operation of said fuel feeding means after combustion has extended sufliciently to cause the energization of said last named thermo-couple. I

6. In combination, a fuel burning device comprising a fuel supporting surface, means for feeding fuel onto said supporting surface, electrically operated means controlling the operation of said fuel feeding means and effective when energized to cause fuel to be supplied by said fuel feeding means, energizing means for said controlling means including a pair of opposed thermo-couples disposed to extend into fuel located on said fuel supporting surface, one of said opposed .thermo-couples having the junction thereof located adjacent the point at which fuel is supplied to said surface so as to be energized so long as there is any combustion whatsoever and the other of said thermo-couples having the junction thereof located adjacent a point on said supporting surface sufficiently remote from the point at which fuel is supplied thereto so as to be energized only when combustion has extended suificiently far to insure continued combustion without the immediate addition of further fuel, and further means responsive to the condition of a space heated by said fuel burning device for controlling the operation of said fuel feeding means after combustion has extended sufficiently to cause the energization' of said last named thermo-couple.

7. In combination, a fuel burning device comprising a fuel supporting surface, means for feeding fuel onto said supporting surface, electrically operated means controlling the operation of said fuel feeding means and effective when energized to cause fuel to be supplied by said fuel feeding means, energizing means for said controlling means including a pair of opposed thermo-couples disposed to extend into fuel located on said fuel supporting surface, one of said opposed thermo-couples having the junction thereof located adjacent the point at which fuel is supplied to said surface so as to be energized so long as there is any combustion whatsoever and the other of said thermo-couples having the junction thereof located adjacent a point on said supporting surface sufiiciently remote from the point at which fuel is supplied thereto so as to be energized only when combustion has extended sufficiently far to insure continued combustion without the immediate addition of further fuel and means responsive to a temperature produced by said device for terminating the operation of said fuel feeding means when said. temperature reaches a value above a predetermined upper limit.

8. In combination, a fuel burning device, means for regulating the admission of fuel to said device, means including an electromagnet for controlling said fuel regulating means and adapted when energized to cause said fuel regulating means to supply fuel to said device, and means comprising a plurality of opposed thermo-couples for controlling the energization of said electromagnet, one of said thermo-coupies being responsive to a condition indicative of the presence or absence of any combustion and the other to a condition accompanying a temperature above a predetermined upper limit.

' temperature 9. In combination, a fuel burning device, means for regulating the admission of fuel to said device, said means comprising a plurality of opposed thermo-couples one of said thermocouples being responsive to a condition indicative of the presence or absence of any combustion and the other to the existence of a condition accompanying a temperature above a predetermined upper limit, said thermo-couples generating counter electromotive forces when both are indicating the presence of combustion.

10. In combination, a fuel burning ,device, means for regulating the admission of fuel to said device, means including an electromagnet for controlling said fuel regulating means and operative upon energization of said electromagnet to cause said fuel flow regulating means to supply fuel to said device, a thermo-electric device operative upon the presence of combustion to cause said electromagnet to be energized and a second thermo-electric device operative upon the existence of a condition accompanying a temperature above a predetermined upper limit to oppose the action of said first thermo-electric device and deenergize said magnet.

11. In a temperature regulating system, temperature changing means, means including an electromagnet controlling said temperature changing means and effective upon energization of said electromagnet to cause the operation of said temperature changing means, said electromagnet comprising a main winding and an auxiliary winding, 2. thermo-couple controlling the energization of said main winding, the junction of which when heated energizes said main winding, and means operative upon said tem-.

perature changing means being placed in operation by reason of the energization of said first winding to effect the energization of said auxiliary winding.

12. In combination, a fuel burning device having a zone of combustion which varies in extent, means for feeding fuel to said device, and means for regulating said fuel feeding means, said regulating means comprising temperature responsive devices responsive to the temperatures at various points in the path of the zone of combustion being successively traversable by burning fuel and operative to control said fuel feeding means in accordance with the extent of the zone of com bustion.

13. In combination, a fuel burning device having a zone of combustion which varies in extent, means for feeding fuel to said device, and means for regulating said fuel feeding means, said regulating means comprising thermo-couple means located in the path of the zone of combustion at varying distances from the source of fuel supply and operative to control said fuel feeding means in accordance with the extent of the zone of combustion.

14. In combination, a solid fuel burning furnace, a stoker for supplying fuel to said furnace including a stoker motor, means for terminating operation of said stoker motor upon there being no combustion or excessive combustion and for causing the operation of said stoker motor when combustion is at a minimum value, said means comprising devices responsive to the presence or absence of combustion in the fuel bed at varying points from the center of combustion and accordingly responsive to the spread of combustion.

15. In a temperature regulating system, tem perature changing means, a controller for said changing means including a thermo-coupie for energizing the same, said controller being effective upon energization thereof to cause said temperature changing means to be brought into operation, and means effective upon energization of said controller and upon the resultant operation of said temperature means to additionally energize said controlling means so that the temperature difference between the hot and cold junctions of said thermo-couple must decrease below the value required to effect the energization of said controller before said controller is effectively deenergized.

16. In a temperature control system of the class described, temperature changing means, an electrically operated regulator therefor, a switch controlling said regulator and normally resting in a predetermined circuit controlling position, means to periodically move said switch back and. forth without changing its circuit controlling position, said means comprising pusher means associated with said switch and comprising a pivoted arm biased to one position, continuously running means adapted to periodically engage said arm and move said switch through ,said pusher means, an electromagnet member and an armature member, one of said members operated by said means to periodically urge the same against the other of said members, a thermo-couple responsive to a temperature of said system and operative when said temperature is above a predetermined value to energize said electromagnet sufficiently to maintain said members adjacent each other when so moved by said means but incapable of causing movement of said members adjacent to one another when they are spaced from each other, and means to move said switch to another circuit controlling position when said members are held adjacent each other by the action of said continuously running means to the position in which said members would otherwise be moved apart, said movement of said switch being effective to move the pusher means to a position wherein said arm when resting in the position to which it is biased will not be engaged by said continuously running means.

17. In combination, a fuel burning device hav-,

ing a zone of combustion which varies in extent, means for feeding fuel to said device, and means for regulating said fuel feeding means, said regulating means comprising temperature responsive devices responsive to the temperature at various points in the path of the zone of combustion, being successively traversable by burning fuel and operative to control said fuel feeding means in accordance with the extent of the zone of combustion, said temperature responsive devices being so constructed and mutually related as to produce a response when the boundary of the zone of combustion moves to a position between them so as to expose them to substantially different temperature.

18. In combination, a fuel burning device having a zone of combustion which varies in extent, means for feeding fuel to said device, and means for regulating said fuel feeding means, said regulating means comprising thermocouple means located in the path of the zone of combustion at varying distances from the source of fuel supply and operative to control said fuel feeding means in accordance with the extent of the zone of combustion, said thermocouple means being so mutually related as to produce a response when the boundary of the zone of combustion recedes or advances from a position between them so as to expose them to temperatures of similar magnitude.

19. In combination, a solid fuel burning furnace, a stoker for supplying fuel to said furnace including a stoker motor, means for terminating operation of said stoker motor upon there being no combustion or excessive combustion and for causing the operation of said stoker motor when combustion is at a minimum value, said means 10 comprising devices responsive to the presence or absence of combustion in the fuel bed at varying points from the center of combustion and acoordingly responsive to the spread of combustion, said devices being so constructed and mutually related as to produce a response when the boundary of thezone of combustion moves to or from a position between them. 

